This invention relates generally to a hydraulic braking system and, more particularly, to such a system for a rail vehicle such as a rapid transit car.
Traditionally, railway vehicles have used air braking systems. These air braking systems have been developed to a point where they operate quite well for long haul freight and passenger train applications. However, the advent of rapid transit systems has developed the need for more precise braking of the rapid transit cars than can be achieved with air brakes.
In response to this need, hydraulic braking systems for railway vehicles have been developed. An example of one such hydraulic braking system is shown in U.S. Pat. No. Re 29,096. The braking system shown in that patent utilizes relatively incompressible hydraulic fluid rather than compressible air. Therefore, more precise braking control can be gained through the use of hydraulic fluid, as explained in that patent. The braking system shown in that patent has proved to be very effective in meeting the demanding operational requirements of the Washington Metro Transit System.
Braking pressure in the hydraulic braking system of U.S. Pat. No. Re 29,096 is regulated by a pilot pressure controlled brake control valve. Pilot pressure is varied by variably restricting the outflow of a constantly flowing pilot fluid. Although the system works quite well, the power required to maintain the constant flow of pilot fluid is excessive.
It is therefore an object of this invention to provide a hydraulic braking system for a rapid transit vehicle which minimizes power demands and which can be used with hydraulic or pneumatic controls and with a variety of brake actuators.